DOCS: add typehints

[jkowalleck]

current implementation is untyped undocumented javascript

as a user of this library i want type docs, so that i know expected parameter types. as a user of this library i want type docs, so that i know possible throws. as a user of this library i want type docs, so that i know possible return types. as a user of this library i want type docs, so that tools/IDE assistance is improved.

options:

• rewrite the whole thing in typescript.
• add jsdoc to methods, properties, classes,
• add type definition files (*.d.ts) to the project

enforce typehints via eslint rules: https://github.com/gajus/eslint-plugin-jsdoc